A dog clutch is a mechanism used to connect and disconnect two rotating shafts or machine parts. The dog clutch functions by mating a set of regularly spaced teeth or protrusions on one half of the clutch mechanism to a set of identical recesses on the other rather than the friction principle used in other clutches. This has the benefit of allowing both shafts to turn at the same speed without slipping and with minimal clutch wear. They can not, however, be used to control torque as is the case with a friction clutch. Dog clutches are commonly used in manual or stick shift automobile gearboxes, marine propeller drives, and on the drives of heavy machinery.

A dog clutch typically consists of round plates, one fixed to the drive shaft and one to the driven shaft. One of the plates has a series of evenly spaced protrusions machined into its face similar to the battlements on top of a castle wall. The other has an identically spaced series of like sized recesses cut into its face. When the two plates are brought together, the protrusions mate or fit into the recesses, thereby effectively joining the shafts and transferring rotational motion from one to the other. This ensures a strong mechanical coupling between the two components with no slip characteristics.

Due to the lack of slippage in a dog clutch, the clutch mechanism is not subjected to the amount of wear and tear that is encountered with friction clutches. It does, however, not allow for the gradual initiation of the drive process and resultant torque control that a friction clutch does as the drive engagement is immediate. This type of clutch arrangement allows for a strong, reliable transfer of rotational motion between components using a minimum of moving parts and constant maintenance of equal shaft speeds.

One of the most common uses of a dog clutch is the drive engagement of individual gears in a manual automobile gearbox. When different gears are selected in this application a synchromesh system allows the drive and selected gears to mesh smoothly using a dog clutch system. Most marine stern drive and outboard engines use dog clutches in their gear trains as do bicycle hub gear assemblies. Large dog clutch arrangements are also commonly used in the main and auxiliary drive trains of heavy machinery such as excavators where no clutch slippage is essential. Another well known use of this type of clutch is the cord pull-start system on gasoline engines.